Steric hindrance in potassium atom-oriented molecule reactions. Methyl iodide and tert-butyl iodide

TLDR: In this article, the reaction of K atoms with oriented CHJ or t-CqH9I molecules has been studied via the crossed molecular beam method and it is shown that the hindering size which can be ascribed to the R groups is only roughly compatible with van der Waals radii.

Abstract: The reaction of K atoms with oriented CHJ or t-CqH9I molecules has been studied via the crossed molecular beam method. Oriented molecules are produced by passing a molecular beam through an inhomogeneous electric field which rejects unwanted orientations. The remaining molecules are oriented with respect to a weak electric field and can be reversed in the laboratory by changing the direction of the applied field, The reaction is studied for impact a t the two ends of the molecule and for both reactions the iodine end is most reactive. A simple model is used to interpret the results and suggests that the hindering size which can be ascribed to the R groups is only roughly compatible with van der Waals radii. Very few gas phase bimolecular chemical reactions proceed on every gas kinetic-collision. Most reactions have an activation energy which (presumably) restricts reaction to those collisions with energy greater than the activation energy, E,. But counting only those collisions with energy greater than E , still gives a rate faster than the rate of almost any chemical reaction. To account for this discrepancy between theory and fact the notion was advanced that only certain orientations of the reagents were effective in promoting reaction, and the “steric factor”, p , was introduced as the fraction of gas-kinetic collisions which had the right orientation to react. Journal of the American Chemical Society / 97:7 / April 2, 1975